[IWeldMelons]

Soda is not "very acidic", for the exception of coke, which has strong acid added to it. Carbonic acid is very weak, and won't prevent bacteria from growing.

[cyberax]

Carbonic acid has a pH of around 4 in sodas. Stomach acid is 3. Both are enough to discourage bacterial growth.

It doesn't prevent _all_ bacteria, as I said. But it prevents most of pathogenic bacteria.